10^320236 + 10^160118 + (137×10^160119 + 731×10^159275) × (10^843 − 1)/999 + 1 is the largest known palindromic prime number. This number is so large that if you started to write it in long form, you wouldn't be finished for quite a while, and might even lose track of how many digits you have written. A number being palindromic means it remains the same when it's digits are reversed. Humans cannot reverse their digits, though they can have some increase in flexibility if they are double jointed. They also have reversible clothing, but only numbers have true reversible digits.
10^150006 + 7426247×10^75000 + 1 is the largest known happy palindromic prime. A happy number is a number where you can replace the number by the sum of the squares of it's digits until the number equals one. If a number doesn't resolve to 1 in this manner it is called an unhappy, or a sad number. Scientists don't understand why this makes a number happy or sad yet, because to date, they have been unable to find a number with a nervous system at all!
